Bitumen is a common material utilized in the preparation of paving, roofing and coating materials. While the material is suitable in many respects, it is inherently deficient in some physical properties. It is highly desirable to improve upon these physical properties. Diene polymer rubbers such as styrene-butadiene rubber and styrene-rubber block copolymers such as styrene-butadiene-styrene and styrene-isoprene-styrene block copolymers have been added to bitumen in the past to dramatically improve the thermal and mechanical properties of bitumens.
Bitumen emulsions and dispersions have also been known for some time. These emulsions and dispersions are characterized as heterogeneous 2-phase systems consisting of two immiscible materials, bitumen and water. The bitumen is dispersed throughout the continuous water phase in the form of discreet globules which are held in suspension by an emulsifier. Such bitumen emulsions and dispersions have a wide variety of uses such as in road construction, horticultural and agricultural applications, slip coats for concrete, protective coats for concrete, pipelines and ironwork and also for sealing cracks and grouting.
Bitumen emulsions and dispersions that contain polymers are also known. Polymer modification of such emulsions and dispersions gives the same advantages to emulsions and dispersions as to bitumen alone. It is common practice to store emulsions for a period of time between the time of manufacture and the time of application. However, such modified emulsions and dispersions have the disadvantage that they are often not sufficiently stable (they may coalesce, irreversibly flocculate or settle or cream), the coalesced bitumen phase has poor properties after water drying and they are difficult to prepare at high polymer loading. Thus one objective for a successful emulsion is that it be stable during the storage time. With regard to storage stability, polymer modified emulsions often exhibit phase instability which manifests itself in terms of bulk phase separation. Upon standing for long periods of time, different phases may form: a lower or bottom phase that exhibits an increased percentage of dispersed (bituminous) phase and an upper or top phase that exhibits an increased percentage of aqueous phase. As used throughout the present specification, the phrase “storage stability” refers to this phase separation phenomenon.
It is also known to make emulsions and dispersions of polymers in water with a surfactant and then to add the resulting polymer emulsions and dispersions to bitumen in order to obtain improved properties. Addition of a polymer emulsion or dispersion to bitumen provides a means of mixing polymer and bitumen which does not require special high shear high temperature mixing equipment. It does not put the polymer and bitumen through an unnecessary heating step. However, when this process is used, it is often difficult to prepare modified bituminous emulsions and dispersions which demonstrate a good balance between storage stability, viscosity and breaking rate after application, thereby resulting in a product that is stable and easy to apply.
Therefore, there is a need for bitumen emulsions and dispersions that have an increased degree of storage stability and are relatively easy to work with and apply. The present invention provides such emulsions and dispersions.